1. Field of the Invention
The present invention relates in general to brakes provided by automotive internal combustion engines, and more particularly to engine brakes of a compression release type, that is, usually called exhaust brakes.
2. Description of the Prior Art
The compression release type exhaust brake is a brake wherein each exhaust valve of the engine is crack opened at the end of each compression stroke when the brake is in operation. That is, when the exhaust valve is crack opened at the end of the compression stroke, part of compressed gas in the combustion chamber is exhausted. Thus, in the subsequent expansion stroke, repulsion applied to the piston is lowered due to reduction of the gas in the combustion chamber. Furthermore, since, after effecting the crack opening, the exhaust valve is kept closed during the expansion stroke, the combustion chamber produces a resistance against the movement of the piston toward a lower dead center. Thus, in the expansion stroke, the force for rotating the crankshaft in a normal direction is reduced resulting in that the engine rotation is lowered or braked.
In order to appropriately operate each exhaust valve in the above-mentioned manner, Japanese Patent First Provisional Publication 9-184407 proposes a mechanism including an exhaust rocker arm which is swingably actuated by an exhaust cam for operating the exhaust valve, a brake rocker arm which is swingably actuated by a brake cam and a coupling structure through which the two rocker arms are operatively coupled. That is, under normal operation of the engine, the exhaust valve is actuated by only the exhaust rocker arm, and upon need of the exhaust braking, the coupling structure couples the two rocker arms causing the exhaust valve to be actuated by the brake rocker arm as well as the exhaust rocker arm.
However, due to its inherent construction, the above-mentioned conventional exhaust brake fails to exhibit a satisfied function. That is, in this conventional exhaust brake, during the operation, the associated engine is subjected to a marked change in inertia mass of a valve actuating mechanism between two cases, one being a brake case wherein the brake rocker arm is in operation for effecting the exhaust braking and the other being a normal case wherein the brake rocker arm is not in operation. Such marked change tends to induce a non-smoothed movement of the exhaust valve.